Considerations

Broken solar cells for sale on ebay are literally what they are sold as. Broken. It can be a hassle to handle the brittle and split cells without damaging them further.

The bonding wire between the cells have to be light, flexible and able to carry the current of the panel.

Careful measurements under exact same conditions are necessary to match the uneven and broken cells to get a optimal panel from the broken lot.

Specifications

Voltage (optimal load)

14,6 VDC

Current (optimal load)

666 mA

Power output (optimal load)

9.7 Watt

Size

100 x 40 x 3 cm

Schematic

Construction

24th May 2012

I bought a lot of “50 + more free” solar cells, the cheapest I could find on ebay, which at the time was around 10 Euro.

First thing to do was sorting the cells into stacks according to physical conditions. A stack of square cells that had no apparent damage, another stack of slightly kinked squares with broken corners, another stack of cells with larger missing parts or split cells and last a stack of completely broken or trashed cells.

To measure the electrical properties I waited until night and sat in a room with a single light source, a 60W incandescent lamp distanced 25 cm to the cell under test. Each cell was measured short circuit through the digital multimeter’s 3 Ohm resistance.

Green is the stack of good cells, yellow the slightly kinked cells and red the cells with larger damages or missing parts.

24th May 2012

The frame is made from 25×25 mm extruded aluminium profiles and acrylic glass front and back.

Each cell is glued to the frame back plate with the same glue described below. It is soft and will give some suspension to the cells, so they are able to move slightly with the frame being handled and thus prevent the cells from splitting or cracking.

A lot of black industrial grade glue / silicone is used for ensuring that the panel is water tight and some bags of silicon gel beads are left inside to take care of any moisture, to prevent fog on the inside.

2nd July 2012

Panel performance measurements with panel aimed 90 degrees upon the sun, in the evening at 19:30. A variable 100 Ohm 100 Watt resistor was used to load the panel and voltage / current measurement was taken.

Voltage

Current

Wattage

18 V

235 mA

4,23 W

17,8 V

284 mA

5,05 W

17,6 V

322 mA

5,67 W

17,4 V

352 mA

6,13 W

17,2 V

394 mA

6,78 W

17,0 V

389 mA

6,61 W

16,8 V

410 mA

6,88 W

16,6 V

452 mA

7,5 W

16,4 V

515 mA

8,45 W

16,2 V

532 mA

8,62 W

16,0 V

557 mA

8,91 W

15,8 V

576 mA

9,1 W

15,6 V

596 mA

9,30 W

15,4 V

615 mA

9,47 W

15,2 V

629 mA

9,56 W

15,0 V

646 mA

9,69 W

14,8 V

653 mA

9,66 W

14,6 V

666 mA

9,72 W

14,4 V

672 mA

9,68 W

14,2 V

678 mA

9,63 W

14,0 V

683 mA

9,56 W

Wattage is calculated and as it can seen the panel performs best at 14,6 VDC out at 666 mA, giving 9,72 Watt.

Plotting the measurements it is easier to see where the curve bends downwards again.

Battery charging test

To be made when I have a battery charger / inverter setup.

Conclusion

More than 3 years have passed since I bought and built this solar panel. Now you can buy 10 Watt panels with chargers and cable for maybe double of what I spent on building one from scrap components.

The physical size of my panel also gives it a much lower power density than commercial available panels. I did also expect more of the cells to start with.

Building solar panels yourself does seem like there is no longer a great cost to cut in doing so. The mass production and leaps forward in technology have dropped the prices on the first widely available generations of solar cells.

There certainly is no idea in building your own low power panels, there might still be a leverage on building high power panels with pristine solar cells to start with.

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